It is known that an intervertebral disk may undergo changes such as compression, deformation, shift or wear and, more generally, degeneration associated with mechanical stress on it and leading to anatomic and functional destruction of the vertebral disk and segment. This disk alteration modifies the mechanical behaviour of the disk and results in a reduction in the height of the intersomatic space, in turn perturbing the functional articular unit. This results in instability, in particular inducing an arthrosis reaction, a source of pain and osteophytic processes. In the same way, nucleus pulposus herniation may arise, requiring the removal of the cervical disk.
Therefore, a proposal was made to replace the defective disk with an artificial disk and several types have been considered. For example, in particular U.S. Pat. No. 5,562,738 a disk prosthesis for lumbar vertebrae comprising first and second fixation plates to neighbouring vertebrae, made of a metal such as titanium. An articulation knob is inserted between the plates, comprising a first insert assembled on one of the plates and consisting of a spherical cap co-operating with a spherical cup from a second insert assembled on the other plate. The inserts are made of a biocompatible ceramic presenting improved tribology characteristics, in particular as regards the capacity of resistance to wear.
However, such a disk prosthesis for lumbar vertebrae is not suitable to replace the disk of cervical vertebrae since such a prosthesis does not allow the cervical vertebrae to recover their natural mobility. In addition, the shape of the articulation knob is relatively difficult to produce properly and is sensitive to break and crack phenomena, thereby reducing the life of the prosthesis.
Therefore, the purpose of the present invention is to rectify the disadvantages of the prior art by proposing a disk prosthesis for cervical vertebrae designed to present a relatively long life span by being practically insensitive to wear and break phenomena, while being adapted to authorise physiological mobility between the two equipped cervical vertebrae.